During the analysis process of a sample by using Gas Chromatography (GC) or a GC combined to ion mobility spectrometer (IMS)/Mass Spectrometer (MS), the sample passes through a sample injector first. The sample injector is used for rapid vaporizing the liquid or solid sample of interest at a first place and then feeding the sample vapor to a GC column head quickly, accurately and quantitatively after mixing and diluting with the carrier gas. Since the first capillary column has been produced by Perkin Elmer, due to its advantages of high column efficiency and good separation performance, there has been already more than 90% of GC analysis realized by capillary columns nowadays (“Basic Gas Chromatography”, Second Edition, by Harold M. McNair and James M. Miller. Copyright© 2009 John Wiley & Sons, Inc.). Due to the characteristic of small capacity of a capillary column itself, split/splitless sample injectors have become the most common sample injectors for GC, GC-IMS or GC-MS.
There have been mature split/splitless sample injectors at present. However, as different sample components have different actual split ratios, under a certain set separation ratio, the component entering a chromatographic column (capillary column) will be different from the original sample component so as to result in split discrimination (especially for samples having a wide boiling range), so that the accuracy of analysis is influenced to result in poor quantification and complexity.
There are mainly three aspects for the cause of the split discrimination:
First, non-uniform heating temperature distribution of a vaporizing chamber: in some cases, a difference between the temperature at the center of the vaporizing chamber and the temperature at two ends thereof is very large, so the sample is not vaporized uniformly or components having different boiling points are coagulated at positions below the point of vaporization point after being vaporized.
Second, the carrier gas is not preheated: the carrier gas will have a change in temperature gradient after entering the vaporizing chamber, so the vaporization rates of different components of the sample will be different; as the time the sample enters the chromatographic column from vaporizing in the vaporizing chamber is very short (in seconds), so that the split flow is far larger than the flow in the column, and thus the components not fully vaporized may split more samples than the components fully vaporized.
Third, different sample components have different diffusion rates in the carrier gas; however, the diffusion rate is in direct proportion to the temperature, so vaporizing the sample as quick as possible is an important measure for reducing split discrimination. Therefore, the temperature of the sample injector must be strictly controlled and is slightly higher than the temperature of the column oven; thus, the manufacturing cost of the sample injector is improved, and it is disadvantageous for the analysis of thermally instable substances.
Patent No. CN1352390A has disclosed a sample injector for solving the preheating problem of carrier gas. In the sample injector, a carrier gas preheating chamber is provided between a split flow exporting channel and a vaporizing chamber, a carrier gas inlet is communicated with the lower portion of the carrier gas preheating chamber, and the upper portion of the carrier gas preheating chamber is communicated with the vaporizing chamber. The carrier gas enters the carrier gas preheating chamber from the inlet and then moves upward after preheated, and then enters the vaporizing chamber from the top to contact a sample and vaporize the sample instantly. Although such a sample injector port solves the preheating problem of carrier gas and the problem of split discrimination, the volume of the vaporizing chamber is increased equivalently as the preheating chamber is communicated with the vaporizing chamber, that is, the pre-column dead volume is increased. Thus, the vaporized sample mixture gas will be diffused back to the preheating chamber, thereby increasing retention time (RT) and broadening peak.
To overcome the problems in the patent CN1352390A, Patent No. CN203216933U has disclosed a sample injector for non-volatile substances, including a shell and a diffusion tube disposed inside the shell. A carrier gas channel communicated with the diffusion tube is provided on an end cover of the shell. The carrier gas channel extends to the inside of the diffusion tube and has a certain distance away from the bottom of the diffusion tube. The advantage of this design is that, as the sample is placed on the bottom of the diffusion tube, the volatilization concentration on the surface is the highest during the volatilization of the sample; and the carrier gas channel extends above the surface of the sample, so the carrier gas may take away all the volatilized gas on the surface of the sample. In order to uniformly heat the upper and lower portions of the sample injector, electric bars extending from the bottom of the shell to the end cover are uniformly arranged around the shell of the sample injector, so that uniform heating of the upper and lower portions of the sample injector is realized. In the parent, the problem of non-uniform vaporizing of the sample is solved, but the sample injector has a splitless mode only. As the splitless sample injection mode has complicated operating conditions and high requirements for operation techniques, the splitless sample injection is far less common than the split sample injection in practice. Therefore, the splitless sample injection is taken into consideration only when the split sample injection cannot meet the analysis requirements (mainly requirements for sensitivity).
In addition, it is required to perform continuous sample injection when a detection task is heavy, and it is required to reset temperature of a sample injector in the case of an obvious difference between boiling ranges of samples at two adjacent times. Although there are various split/splitless sample injectors of different types, yet there are few general sample injectors capable of cooling fast. Therefore, in order to realize fast testing, it is necessary to add a fast cooling design and a temperature control design to a general sample injector.